Chlamydia trachomatis and C. pneumoniae are intracellular bacteria that are responsible for several serious diseases. As well as blinding eye infections, the former causes chronic sexually transmitted infections that can result in infertility, and the latter causes often asymptomatic and undetected respiratory infections associated with the development of atherosclerosis. Fan et al.show that these bacteria secrete into the host cell factors that induce degradation of a host transcription factor known as RFX5. This component is required for a key stage in the processing of foreign material by host cells, because it promotes the expression of major histocompatibility complex antigen (MHC). If MHC cannot be expressed on the host cell surface in combination with peptide fragments from the pathogen, then the pathogen will remain undetected by host's immune surveillance machinery. However, it is not yet known how the chlamydial factors themselves evade immune surveillance. — CA